(1) Field of the Invention
The present invention relates to an internal combustion engine.
(2) Description of Related Art
A gasoline engine performs cylinder injection of fuel in three processes consisting of spark, ignition, and flame propagation.
The flame of combustion gas ignited and combusted at substantially the center of a combustion chamber propagates at a high speed to immediately spread over the combustion chamber.
If the flame spreads over the combustion chamber, burned gas combusted by the flame of the combustion gas pushes unburned gas components in unburned fuel gas to an area in the vicinity of a wall of the combustion chamber, and the unburned gas components are gradually combusted in the expansion stroke.
Incidentally, the unburned gas components pushed to the area in the vicinity of the wall of the combustion chamber by the burned gas is then brought into contact with a wall of a cylinder as the wall of the combustion chamber, or enters a piston crevice between a piston and the cylinder. On this occasion, a quenching phenomenon occurs in which the unburned gas is deprived of heat by the wall of the combustion chamber to be decreased in temperature, which inhibits the progress of combustion in the expansion stroke.
If the combustion of the unburned gas components is inhibited as described above, unburned gas components such as HC, CO, and so froth remain on the wall of the cylinder or the surface of the piston, or in the vicinity of the piston crevice even after the completion of the expansion stroke. The remaining unburned gas components (such as HC, CO, and so forth) are discharged directly into an exhaust passage in the exhaust stroke.
Further, if liquid fuel has not been satisfactorily carbureted, the fuel and the air cannot be mixed sufficiently and thus a part of the combustion gas has an excessively rich air-fuel ratio. Therefore, unburned gas components such as HC, CO, and so forth remain, or smoke and so forth are generated.
It is therefore an object of the present invention to provide an internal combustion engine that is capably of reliably combusting unburned gas components, smoke, and so forth, which are remained in a combustion chamber due to the quenching phenomenon and insufficient mixture of air and fuel.